1. Field of the Invention
The invention generally relates to a system and method for the testing the vision of a subject. More particularly, the invention relates to a system and method for testing the dynamic visual acuity and gaze stabilization of a subject.
2. Background
People maintain their upright posture and balance using inputs from proprioceptive, vestibular and visual systems. During normal daily activity, where dynamic balance is to be maintained, other factors also matter. These factors are visual acuity, reaction time, and muscle strength. Reaction time and muscle strength are important to be able to recover from a potential fall. Visual acuity is important to see a potential danger.
In general, a test for measuring visual acuity (VA) is concerned with measuring the acuteness or clearness of a subject's vision. A test that is specifically designed to measure a subject's dynamic visual acuity focuses on the subject's ability to visually discern fine details in an object while of the head of the subject is being displaced at a generally constant velocity, while a gaze stabilization test focuses on the ability of a subject to ascertain details of an object while his or her head is being displaced over a range of different velocities.
Conventional tests for measuring dynamic visual acuity and gaze stabilization require the distance from the subject to the display screen to be accurately determined. As such, either this distance must be measured each time the test is performed, or alternatively, the distance must be initially measured and then, the placement of the subject relative to display screen must always remain consistent in the testing room in order for the test results to be accurate (e.g., the chair on which the subject is seated during the test and the display screen on which the object is displayed must always be maintained a constant distance apart). Obviously, measuring the distance between the subject and the display screen each time the test is performed is both inconvenient and time consuming for the both the subject and the person performing the test. Also, determining the distance before the performance of each test is particularly problematic when subjects having disorders are being tested. These subjects are especially susceptible to easy fatigue. In addition, it is often very difficult, or even completely impractical, to always maintain a constant distance between each subject being tested and the display screen. After all, the visual testing system may comprise a portable type system that is moved from site to site, and set up in different locations each time the test is being performed. In such a portable situation, it is virtually impossible to maintain a constant distance between the location of the subject and the display screen. Thus, it is necessary to measure this distance each time the testing arrangement is set up. Even if the testing arrangement is not portable, and always in the same testing room, it is still very difficult to maintain a constant distance between the subject and the display screen. For example, if subjects are seated on a chair during the vision test and the chair is not fixed in place, subjects will most likely displace the chair when they get up from the seated position after completing the test, thereby shifting the position of the chair relative to the display screen. This movement of the chair will require the distance between the subject and display screen to be determined again.
What is needed, therefore, is a system and method for testing the dynamic visual acuity and gaze stabilization of a subject that does not require the measurement of the exact distance between the subject and the display screen. Moreover, a system and method for testing the dynamic visual acuity and gaze stabilization of a subject is needed that can be easily transported, and set up in different locations, without necessitating the measurement of the exact distance between the subject and the display screen at each of the different testing locations. Furthermore, a need exists for a system and method for testing the dynamic visual acuity and gaze stabilization of a subject that is capable of being quickly implemented, and produces accurate results as long as the relative location of the subject to the display screen remains generally constant during a particular test session.